1. Field of the Invention
The invention relates to a hydrodynamic clutch arrangement which is used to establish and to release a working connection between a drive and a takeoff.
2. Description of the Related Art
A hydrodynamic clutch arrangement of this type, which is known from FIG. 5 of DE 103 58 902 A1, is used to establish and to release a working connection between a drive, such as the crankshaft of an internal combustion engine, and a takeoff, such as a gearbox input shaft, and is designed with a housing, which is free to rotate around an axis of rotation. In DE 103 58 902 A1, the clutch arrangement is designed as a hydrodynamic torque converter, in which a hydrodynamic circuit is provided with a pump wheel, a turbine wheel, and a stator, which together form a torus volume (TV) enclosed by a torus space. In addition, the hydrodynamic clutch arrangement is provided with a bridging clutch, by means of which the hydrodynamic circuit can be bypassed with respect to the transfer of torque from the drive to the takeoff, where a torsional vibration damper with two sets of circumferential springs is assigned to the bridging clutch to damp torsional vibrations. The bridging clutch and the torsional vibration damper together form a mechanical transmission circuit, which is located inside a clutch space of the housing, where a clutch volume (CV) is determined by this clutch space.
The hydrodynamic torque converter shown in FIG. 5 of DE 103 58 902 A1 is evidence of a development trend, frequently observed in recent years in hydrodynamic clutch arrangements, according to which the size of the torus space is limited so that the clutch arrangement will fit in a more compact space. There are also trends toward increasing the number of plates in the bridging clutch so that higher torques can be transmitted and toward installing more powerful and therefore more complicated torsional vibration dampers. Because these larger components occupy a considerable amount of room in the clutch arrangement, a larger clutch space is required. FIGS. 1-3 are attached to the present specification to make it easier to understand the explanation of the relevant spaces present in a hydrodynamic clutch arrangement, i.e., the spaces which define the corresponding volumes. FIG. 1 shows the torus volume (TV); FIG. 2 shows the clutch volume (CV); and FIG. 3 shows the resting volume (RV). The resting volume (RV) is present after a minimum resting phase, during which some of the fluid in the hydrodynamic clutch arrangement sinks under the force of gravity into the part of the housing located underneath the axis of rotation, and the rest of the fluid leaves the housing through the flow routes provided.
When the motor vehicle containing the hydrodynamic clutch arrangement is restarted, centrifugal force begins to distribute the fluid present in the resting volume (RV) throughout the torus volume (TV) and the clutch volume (CV), but at the same time, because the pressure in the torus volume (TV) is positive with respect to that in the clutch volume (CV), at least some of the fluid remaining in the torus volume (TV) is drawn into the clutch volume (CV). This problem is made even worse when the driver shifts the transmission into “Drive” (D), because, as a result, the drive starts to run at a predetermined speed, whereas the takeoff and thus the torsional vibration damper remain essentially at rest. In spite of the applied centrifugal force, this causes fluid to be drawn in the radially inward direction through the torsional vibration damper. If the hydrodynamic clutch arrangement is designed as a two-line system, it is true that, in this operating state, fresh fluid is introduced from a fluid reservoir into the clutch volume (CV) via the opened bridging clutch, but, instead of proceeding initially into the torus volume (TV), this fluid is also drawn radially inward and thus remains in the clutch space. When the vehicle is being started up, these conditions are expressed by the inability of the torus volume (TV), which at this point is still almost completely empty, and of the opened bridging clutch to transmit any significant amount of the torque being introduced by the drive to the takeoff. Only the slip torque of the bridging clutch is able to provide for the transmission of a certain residual torque. It is only as the clutch volume (CV) gradually begins to fill up that fresh fluid begins to be transferred to the torus circuit, and only then does that circuit become filled. A performance characteristic of this type, however, cannot be tolerated in a modern motor vehicle.